Adding Checkbox In Order Status

[Mr.SerikuS]

Hello! I tried several ways, but failed.

 

I need to add checkbox to order statuses "Send SMS"

 

If checkbox is checked, SMS will be sended via API (sms.mygate.mg/apikey=asd&sender=myname&telnum=[prestatelnr]&text=your order[prestaordernum] is ready

if(isset($_POST['sendsms'])) 

{ 
$curl = curl_init('http://sms.mygate.xx/apikey=asd&sender=myname&telnum=[$order->id_order]&text=your order[$order->id_order] is ready');
}